Cold-seal adhesives and comestible packages formed therewith

ABSTRACT

Comestibles are packaged in wrappers formed of plastic film or equivalent sheet material sealed with cold-seal adhesives containing a minor percentage of vinyl-pyrrolidone/styrene copolymer as a bond enhancement agent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates broadly to cold-seal adhesives, packages sealedtherewith and new methods of forming packages. More particularly, itconcerns latex (emulsion) adhesives capable of forming dry adhesivelayers on plastic or equivalent film that can then later be pressurebonded together, without the use of heat, to form wrappers about candyor other comestibles.

2. Description of the Prior Art

It is conventional practice to form packages for many products simply bywrapping the product in paper, metal foil, plastic film or other sheetmaterial. Often, in order to complete the packaging, overlapped layersof the wrapper are bonded together in some way, e.g., by crimpingstabling, cementing, etc.

The bonding of sheet wrappers by cementing overlapped layers with sometype of adhesive is attractive from the viewpoint of cost savings andpackage esthetics. However, this can be restrictive as to the choice ofthe wrapper material if suitable adhesives do not exist for the bondingof certain classes of sheet material. For example, some types of plasticfilms, such as polyolefin film, are difficult to permanently bondtogether with adhesive because adhesives to not stick easily to suchfilms.

Also, the type of product being packaged can limit the choice of wrappermaterial and adhesive. For example, candy and other comestibles requiregovernment approved wrapper materials and adhesive ingredients whicheliminates many materials available for packaging other type products.Moreover, heat sensitivity of some candy and other comestibles mitigateagainst the use of heat in effecting the sealing of wrappers about them.Hence, use of cold-seal adhesives, i.e., adhesives that can cementtogether layers of sheet material without need to apply heat thereto(see U.S. Pat. No. 4,375,383), is extensively used in the wrapperpackaging of candy bars and the like.

The present invention provides new improvements in cold-seal adhesivesthat are particularly useful in the packaging of candy and othercomestibles.

OBJECTS

A principal object of the invention is the provision of improvedcold-seal latex adhesives capable of being used to permanently bondtogether layers of high energy treated polyolefin film.

Further objects include the provision of:

1. New methods of packaging candy and other comestibles.

2. New cold-seal adhesives that can bond together layers of polyolefinfilm with greater bond strength than prior know cold-seal adhesives andthat can do this without need to apply a primer to the film.

3. Such adhesives that provide tamper-evident tearing bonds on all majorpolypropylene films.

4. New forms of comestible wrappers.

5. Cold-seal adhesives possessing good processability on full-scalepresses without foaming or blocking problems.

6. Such adhesives which produce cold sealed bonding of polyolefin filmthat improves with aging, even in the presence of slip agents.

7. New wrapper sealing methods which avoid the need for a primerapplication thereby freeing up a coating station in full-scale pressesfor an additional color printing in the packaging operation.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter; it should be understood, however, that the detaileddescription, while indicating preferred embodiments of the invention, isgiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

SUMMARY OF THE INVENTION

The objects are accomplished, in part, in accordance with the inventionby the provision of cold-seal latex adhesives for use in sealingcomestibles in wrapper packages which comprise an oil-in-water (o/w)emulsion of the following ingredients in the stated approximate weightpercentages:

    ______________________________________    rubber                 25-45%    acrylic polymer        20-25%    tackifier              25-35%    vinylpyrrolidone/       4-8%.    styrene copolymer    ______________________________________

Additionally, these adhesives may contain up to about 1% by weight of asurfactant, up to about 1% by weight of a foam inhibitor, up to about 1%by weight of a dispersion stabilizer, up to about 2% by weight of ananti-oxidant and up to about 2% of an antiblocking agent.

The objects are further accomplished by the creation of new packages forcandy bars and other comestibles comprising a wrapper of plastic film orequivalent sheet material sealed with an adhesive bond resulting from acold-seal latex adhesive having a composition as stated above.

Additionally, the objects are accomplished by new methods of packagingcomestibles which comprise wrapping a comestible in a corona or otherhigh energy treated polyolefin film, especially polypropylene film, andsealing the comestible in the film by the use of a latex cold-sealadhesive having a composition as stated above.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be obtained byreference to the accompanying drawings in which:

FIG. 1 is a perspective view of a candy bar packaged in accordance withthe invention.

FIG. 2 is a sectional view taken on the line II--II of FIG. 1.

FIG. 3 is an enlarged sectional view of a portion of a bonded jointbetween overlapped layers of polyolefin film made in accordance with theinvention.

FIG. 4 is a fragmentary, plan view of a sheet of film bearing portionsof cold-seal adhesive of the invention applied thereto creating awrapper material for forming comestible packages in accordance with theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, the invention provides new adhesivecompositions, package components and methods for the production ofcomestible packages 2 comprising a wrapper 4 of corona treatedpolyolefin film 6 having end closures 8 and 10 and longitudinal bottomclosure 12. The closures 8, 10 and 12 are each formed of abutted filmlayers 6a and 6b sealed together with an adhesive layer 14.

The creation of the final packages 2 begins with the production,typically at a coating plant separated from the packaging plant, of acontinuous set of wrapping material 16. Thus, with the use ofconventional, multi-station printing presses (not shown), a coronatreated polyolefin film 6 has applied thereto at separate stations (notshown) artwork and text 18 in one or more colors and a layer of adhesive14 in a predetermined pattern 20 thereby forming the wrapping material16. The adhesive pattern 20 typically will be rectangular defined bylongitudinal stripes 22 and transverse stripes 24.

The adhesive layer 14 is applied to the film 6, usually after theapplication of the artwork and text 18, by gravure roll application sothat the layer 14 has a thickness of about 0.25 to 0.50 mil and consistsof a multitude of separated spots or dots, rather than solid, continuouslayer.

The adhesive applied to form the layer 14 is a latex cold-seal adhesivein the form of an o/w emulsion of the following ingredients in thestated approximate weight percentages:

    ______________________________________    rubber               25-45%    acrylic polymer      20-25%    tackifier            25-35%    vinylpyrrolidone/     4-8%    styrene copolymer    surfactant           up to about 1%    foam inhibitor       up to about 1%    dispersion stabilizer                         up to about 1%    antioxidant          up to about 2%    antiblocking agent   up to about 2%.    ______________________________________

An example of a latex cold-seal adhesive of the invention consists ofthe following ingredients in the stated solids-dry-weight percentages:

    ______________________________________    Natural rubber latex (62% solids)                               40%    "GY GNL 150" (Goodyear)    Pentaerythritol rosin ester emulsion                               30%    "Pentalyn H" (55% emulsion - Hercules)    Acrylic polymer (50% emulsion)                               21.5%    "2600 × 288" (Goodrich)    vinylpyrrolidone/styrene copolymer                               5%    "Polectron 430" (40% emulsion - GAF)    Sodium gluconate (antioxidant component)                               0.5%    Antioxidant (50% emulsion) 0.5%    "Aquamix 334" (Harwick Chemical Co.)    Casein (15% aqueous solution - generic)                               0.5%    (dispersion stabilizer and antiblocker)    Fatty acid amide (antiblocker)                               1.0%    "MichemLube 177" (20% emulsion - Michelman)    Non-foaming surfactant     0.75%    "Surfynol 440" (Air Products & Chemicals Inc.)    Foam inhibitor surfactant  0.25%    "Foamaster III" (Henkle Corp).    ______________________________________

All the above listed ingredients meet FDA requirements No. 176:170 foruse in food wrappers.

The amount of adhesive used in forming the layer 14 for wrappingmaterial 16 will typically be about 0.7 to 1.0 lbs. per 1000 sq. ft. ofapplication. Also, when corona or other surface treated sheet materialis used, the adhesive is applied to the treated surface.

As the wrapping material 16 issues from the coating machine (not shown)with the artwork and text 18 and adhesive layer 14 dried, it is rolledinto a roll (not shown) for storage and/or transport to a comestiblepacking plant. At such packaging plant and using conventional form, filland seal machines (not shown), candy bar packages 2 are produced. To dothis, the packaging machine cuts individual wrappers 4 from the material16 by cutting at a "form" station through the portions 28 of thematerial 16 between two adjacent transverse stripes 24. Then, the candybars 30 are placed at a fill station on the cut film 6, after which, ata seal station, the package 2 is formed by face-to-face lapping ofstripes 22 and stripes 24 together by pressure and without heat to formthe end closures 8 and 10 and the longitudinal closure 12.

In the past, several serious problems have persisted in attempts toprovide the packaging industry with acceptable latex cold-seal adhesivesincluding (a) foaming during roller applications, (b) blocking (stickingtogether of layers in rolls of packaging film bearing a layer of theadhesive), (c) lack of "wetting" of the film by the applied layer oflatex adhesive and (d) unsatisfactory adherence of the dried cold-sealadhesive layer to the packaging film. The new adhesives of the inventionsubstantially eliminate these problems in the production and usepolyolefin packing film in packaging of candy or other comestibles.

In preferred embodiments of the invention, the sheet material used forforming packages is polyolefin film formed by casting, blowing,calendaring, etc., particularly, polyethylene and polypropylene film ofabout 0.5 to 2 mil thickness that has received a high-energy (34-40dynes/grms/sq.cm.) treatment, e.g., corona discharge or flame treatment,on one surface thereof. Film that has received such treatment on bothsurfaces should be avoided in order to minimize blocking problems inrolls of the adhesive coated package film. However, if film so treatedon both surfaces is used, antiblocking agents can be included in the newcold-seal adhesives to mitigate the blocking problem.

Advantageously, the polyolefin film is bidirectionally oriented, e.g.,by stretching. Further, the invention is noteworthy for use with film ofthe "high slip" variety produced by inclusion of a slip agent in itscomposition since the new cold-seal adhesives of the invention do notrequire the use of a primer layer in order to "stick" to such film, incontrast to the need for primers to get prior know adhesives to adhereto such film.

In addition to polyolefin film, sheet materials for use in the inventioninclude glassine, metal foil, polyester film, paper, polyvinylidenechloride film, nylon film or equivalent sheet material.

The sheet material can have artwork and text applied in a variety ofways, usually before the application of the cold-seal adhesive.Typically, this will be done using multi-station presses to createdirect or reverse printing of the sheet material. In some cases,especially where water based inks are applied, a lacquer overcoat willbe applied to the printed artwork and text before the application of thecold-seal adhesive.

Rubber is a major component of the new cold-seal adhesives. Since suchadhesive prior to application to sheet material is in the form of an o/wemulsion (latex), it is advantageous to use natural rubber latex,typically containing about 50 to 65% solids by weight, as the source forthis component. Alternatively, synthetic rubber latex may be used, e.g.,styrene/isoprene/styrene block copolymer latex or similar latex.Examples of usable commercially available S-I-S copolymers include"Europene T 190" (Enichem AMERICAS), "Kraton 1112", "Kraton 1320", and"Kraton 1107" (Shell Chemical Company) and S-B-S copolymers include"Kraton 1101" (Shell) and "Stereon 840A" (Firestone Synthetic RubberCo.)

Another essential ingredient of the new adhesives is an acrylic polymer,again supplied in the form of an emulsion, typically containing about 40to 70% solids by weight. A variety of these are commercially availabledesigned for use in pressure-sensitive adhesives, e.g., "2600×288" and"2600×315" (Goodrich). This ingredient provides strength, adhesion andsealing though pressure.

A third essential ingredient of the new adhesives is a tackifier resin,advantageously supplied in the form of an emulsion, typically containingabout 40 to 70% solids by weight. Tackifying resins, also calledtackifiers, useful in formulating pressure-sensitive adhesives (PSadhesives) are a known class of materials and include polyterpeneresins, coumarone-indene resins, hydrogenated hydrocarbon resins,pentraerythritol and other rosin ester resins, hydrogenated rosins andthe like brittle type resins, see U.S. Pat. Nos. 3,027,337, 3,787,531and 3,987,002. Examples of usable commercially available tackifyingresins include "Pentalyn H", "Piccolyte C135", "Foral 85" and"Staybellite Ester 10" (Hercules, Inc.), and "Super Nevtac 99" and"Nevtac 130" (Neville Chemical Co.).

A fourth essential ingredient is a vinylpyrrolidone/styrene copolymer.Such material is commercially available in the form of an aqueousemulsion as "Polectron 430" (GAF Corp.).

Optional ingredients are surfactants, foam inhibitors, dispersionstabilizers, antioxidants, and antiblocking agents. All of these areknown classes of materials for use in adhesives and are commerciallyavailable from a variety of sources under various tradenames.

A preferred surfactant for use in the invention is "Surfynol 440" (AirProducts). Additional surfactants include "Surfynol 104", "Igepal 897"and "Igepal 630" (G.A.F.Corp.) and like relatively non-foamingsurfactants.

A preferred foam inhibitor for use in the invention is "Foamaster III"(Henkle Corp.). Additional foam inhibitors include "Movidyne PA-456" andlike non-silicone products that do not "fish-eye".

A preferred dispersion stabilizer for use in the invention is casein.Additional dispersion stabilizers include polyvinyl alcohol (Dupont),carboxy methylcellulose (Hercules), polyvinyl pyrilodone (GAF) andequivalent water soluble polymeric materials.

A preferred antioxidant for use in the invention is "Aquamix 334"(Harwick Chemical Co.). Other antioxidants useful in the inventioninclude "Irganox 1010" (Ciba-Geigy Corp.), "Ethanox 330" (Ethyl Corp.)and "Borg-Warner 626" and "Borg-Warner TNPP" (Borg-Warner Chemical Co.).

A preferred antiblocking agent for use in the invention is "MichemLube177" (Michelman Co.). Other anti-blockers useful in the inventioninclude stearylamide, behenamide and ethylene bisstearamide. Also, fumedsilica is an effective anti-block agent when used in small quantities.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A cold-seal latexadhesive for use in sealing comestibles in wrapper packages whichcomprises a water dispersion of the following ingredients in the statedapproximate weight percentages:

    ______________________________________    rubber                 25-45%    acrylic polymer        20-25%    tackifier              25-35%    vinylpyrrolidone/       4-8%.    styrene copolymer    ______________________________________


2. The adhesive of claim 1 which additionally contains up to about 1% byweight of a surfactant.
 3. The adhesive of claim 1 which additionallycontains up to about 1% by weight of a foam inhibitor.
 4. The adhesiveof claim 1 which additionally contains up to about 1% by weight of adispersion stabilizer.
 5. The adhesive of claim 1 which additionallycontains up to about 2% by weight of an anti-oxidant.
 6. The adhesive ofclaim 1 which additionally contains up to about 2% by weight of anantiblocking agent.
 7. A cold-seal latex adhesive for use in sealingcomestibles in wrapper packages which consists essentially of a o/wemulsion of the following ingredients in the stated approximate weightpercentages:

    ______________________________________    rubber               25-45%    acrylic polymer      20-25%    tackifier            25-35%    vinylpyrrolidone/     4-8%    styrene copolymer    surfactant           up to about 1%    foam inhibitor       up to about 1%    dispersion stabilizer                         up to about 1%    antioxidant          up to about 2%    antiblocking agent   up to about 2%.    ______________________________________